Abstract: The Importance of Abnormal Pressures in Exploration and Production Geology
Abnormal pressures, both overpressure and underpressure, are typically regarded as a drilling problem, and rarely has the properties of abnormal pressure systems been used to assist in hydrocarbon exploration and production. This paper will how knowledge of abnormal pressures can assist both the explorationist and the production geoscientist. Overpressure is a common phenomenon in the subsurface and is the result of numerous processes, the most important of these are compactional disequilibrium and hydrocarbon generation. An overpressured system will always attempt to equilibrate from the zone of high pressure to low pressure, thus providing a drive mechanism for primary and secondary migration. A knowledge of the overpressure system can indicate the migration pathways, that may be exploited by a Petroleum System. Where the pore pressure intermittently exceeds the fracture gradient, the seal can leak and there will be an alternative migration route, with fluid loss through the seal rather than the spillpoint. The separation between the pore pressure gradient and the fracture gradient can be used to recognize the maximum allowable height of a fluid column with a basin. Details of pressures within a producing field can assist in detecting fault seals and potentially untapped resources.
Therefore, knowledge of the origin and properties of abnormal pressure systems is important to the hydrocarbon geoscientist to assist in both exploration and exploitation of hydrocarbon reserves.
AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria